1. Field of the Invention
The present invention relates generally to a friction clutch, and more particularly to improvements in a friction clutch of the type wherein a clutch disc is disengaged from a flywheel by retracting a releasing member in a direction away from the clutch disc, against the biasing action of a diaphragm spring which acts on a pressure plate to hold the clutch disc in pressed contact with the flywheel.
2. Discussion of the Related Art
In the art of a power transmission system of an automotive vehicle, there is widely known a friction clutch for transmitting a torque from a driving member to a driven member, by means of frictional contact of the driven member with the driving member. An example of such a friction clutch includes (a) a flywheel as a driving member, (b) a clutch cover fixed to the flywheel, (c) a pressure plate disposed between the flywheel and the clutch cover such that the pressure plate is rotatable with the flywheel and clutch cover, and axially movable relative to these latter members, and (d) a diaphragm spring disposed between the clutch cover and a releasing member, such that an intermediate portion of the spring is abuttable on the pressure plate to bias the pressure plate in a forward direction toward the flywheel, for normally holding the clutch disc in pressed contact with the flywheel and the pressure plate, in order to transmit a torque from the flywheel to the clutch disc. The pressure plate is freed from the biasing action of the diaphragm spring by the retracting movement of the releasing member in the direction away from the flywheel, against the biasing force of the spring, whereby the clutch disc is disengaged from the flywheel and the pressure plate. Thus, the friction clutch is selectively placed in its operative and inoperative positions, or the torque is transmitted when needed, from the driving member in the form of the flywheel, to the driven member in the form of the clutch disc. The above friction clutch is called "pull type" wherein the releasing member is pulled to bring the clutch to its inoperative position.
In the friction clutch of the pull type as described above, the releasing member as well as the pressure plate is biased by the diaphragm spring in the forward direction toward the flywheel. Accordingly, if the clutch lining of the clutch disc is excessively worn, or damaged or substantially removed for some reason or other, the releasing member is displaced in the forward direction, together with the pressure plate. This displacement of the releasing member may cause a collision or interference between a release bearing of the releasing member and torsion members of the clutch disc, which bearing and torsion members are positioned closest to each other.
To avoid the above interference, it is proposed to provide the pressure plate with a stopper which is adapted to abut on the clutch cover, in order to prevent an excessive movement of the pressure plate toward the flywheel. Such a stopper is disclosed in Japanese Utility Model Application which was laid open in 1984 under Publication No. 59-77624. The friction clutch disclosed therein is of a push type wherein the releasing member is pushed forward to place the friction clutch in the inoperative position. The stopper indicated above is provided for the sole purpose of preventing plastic deformation of straps which are used to elastically connect the pressure plate to the clutch cover.
It is considered possible to use such a stopper in a friction clutch of the pull type, for limiting a movement of the straps relative to the clutch cover for protecting the straps from plastic deformation. Therefore, the movement of the pressure plate limited by the stopper is relatively large, and consequently the releasing member may collide with the clutch disc when the lining of the clutch disc is excessively worn or damaged. Thus, the use of the stopper in the pull type friction clutch according to the concept disclosed in the above-identified Laid-Open Publication would not solve the problem of collision between the releasing member and the clutch disc.
Of course, it is possible to arrange the friction clutch such that the releasing member and the clutch disc are spaced apart from each other by a distance sufficient to avoid a collision therebetween, even when the pressure plate abuts on the flywheel via the clutch disc upon removal of the clutch lining, or on the stopper for protecting the straps from plastic deformation. In this case, however, it is inevitable that the friction clutch has an undesirably large axial dimension.